1. Field of the Invention
The present invention relates to electronic test equipment used for resistive load testing and, more particularly, to electronic continuity analyzers for resistive load continuity analysis.
2. Description of the Related Art
It is common in many industries to purchase or source parts from various outside vendors. The purchased parts generally must meet various product fabrication and test specifications. These specifications generally become part of the purchase contract/order and thus, the supplier/manufacturer must perform the required tests on the products prior to shipping in order to verify that the products meet the specifications. In many instances equipment has been developed to aid in or totally perform the necessary test(s).
One industry which requires testing of the parts/components it purchases from outside vendors is the U.S. auto industry. What are known as US Car Standards have been developed for the parts/components used by the automotive industry. One type of auto component that requires testing by the purchaser is automotive sockets.
The USCAR/EWCAP PF-1 REV. A standard relates to the testing of lamp sockets, and particularly to the testing of brake light assemblies. In the standard, Section 5.3.4.2 requires that xe2x80x9cthere shall be no loss of electrical continuity, ( greater than =7 Ohms), for more than 1 microsecond on any terminal pair.xe2x80x9d Sections 6.4.4, 6.6.1, and 6.6.2 require that the analyzer should be set xe2x80x9cto record any change in current through the resistor below 95 mA,xe2x80x9d while section 6.4.4.2, step 5 specifies a 120 Ohm resistance and a 12 V DC power supply at 100 mA for the external test circuit. The auto industry will only accept components that successfully pass the tests.
Various types of independent tests may be performed on the electrical component by the test device. Such tests may include thermal shock, vibration, and temperature/humidity testing such as that outlined in paragraph 2.5.2 of the Chrysler Engineering Standard PF-752. These tests can last up to many days. One specified humidity test is thirteen (13) days in length, while one thermal shock test is eight (8) days in length.
Test devices have been developed to aid in the testing procedure. One such device for testing continuity or discontinuity in electrical components is the Bally Intermittence Detector Model #879. This device and others are analog circuits that generally only indicate whether a discontinuity has occurred (i.e. xe2x80x9cpass/failxe2x80x9d) and may also only be used for tests requiring a specific, or internally xe2x80x9chard-wiredxe2x80x9d time period. For these prior art devices it is cumbersome to manually record the total number of failures as is required for many of the tests.
There is a need for a continuity tester that can perform these functions in a more efficient and/or flexible manner.
The present invention is a method and apparatus for analyzing the electrical continuity of a sample load.
The present method detects and counts discontinuities occurring in a load under test. An incoming signal is analyzed to determine if a discontinuity occurs. The discontinuity is counted and a total count is displayed.
In one form, a discontinuity in a sample load is determined by coupling the sample load in circuit with a power source and a known resistance to form a test circuit. A test circuit signal representative of a characteristic of the test circuit is compared to a reference signal. If the comparison results in a discontinuity determination, the discontinuity is counted.
In one embodiment, the time duration of the detected discontinuity is determined and compared to a predetermined time duration. The detected discontinuity is counted only if the detected discontinuity reaches the predetermined time duration. The predetermined time duration is preferably adjustable over a range of values. Further, the discontinuity detection is preferably automatically reset after a discontinuity.
The present apparatus detects and counts discontinuities occurring in a load under test. An incoming signal from the load under test is analyzed by the present apparatus to determine if a discontinuity occurs in the load under test. The discontinuity is counted and a total count is displayed.
In one form, the present apparatus is a continuity analyzer having an input stage that receives a test signal from the load under test and feeds an output signal to a discontinuity detection stage. A detected discontinuity is received by a clocking, counter or time duration comparison stage which determines if the detected discontinuity is of sufficient duration to be considered a discontinuity for test purposes. Any discontinuity signal from the clocking stage is received by a counter stage that tallies the clocking stage signal indicating that a discontinuity was detected. Preferably, a display stage provides visual representation of the total count of detected discontinuities.
In one form, the time duration of the detected discontinuity is determined and compared to a predetermined time duration. The detected discontinuity is counted only if the detected discontinuity reaches the predetermined time duration. The predetermined time duration is preferably adjustable over a range of values. Further, the discontinuity detection is preferably automatically reset after a discontinuity.
In another form, the present continuity analyzer accepts a current input from a test circuit having a load or device under test, and a voltage source as circuit elements. The current through the load is quantified by measuring a voltage drop across a portion of an input resistance. The input resistance is a known quantity such as a 120 Ohm (xcexa9) resistance. A reference voltage is generated and adjusted relative to a standard voltage drop. A discontinuity condition detection means compares the reference voltage to the voltage drop across the input resistance. If the voltage drop across the input resistance drops to within a predetermined value or level relative to the reference voltage, such as to within 0.005V above the reference voltage, a timing sequence of the discontinuity condition detection means commences. This may occur when there is an open circuit, or when the resistance of the load increases by a certain value, such as 7xcexa9. If the voltage does not increase past the predetermined value after a predetermined time period, such as 1 xcexcs, a discontinuity condition is met. A count is then registered and displayed by a display means. However, if the voltage does increase past the predetermined value after the predetermined time period, a discontinuity condition has not been met. At this point, the discontinuity condition detection means is automatically reset to begin detecting a discontinuity.
It is an advantage of the present invention that the total number of failures during a test cycle is determined.
It is another advantage of the present invention that there is an automatic circuit reset.
It is further an advantage of the present invention that the circuit can distinguish whether the load under test had a discontinuity time period long enough to be determined a discontinuity for test purposes.
It is still another advantage of the present invention that it can accommodate varying currents and time periods.
It is further yet an advantage of the present invention that it can count greater than 1 discontinuity for test purposes.